Ouch. A properly made fiberglass piece shouldn't crack that easily. And even if you do manage to damage it, the fiber reinforcement should prevent any damage from spreading. Have you tried contacting the builder? They might be willing to repair/reinforce it for little or no charge beyond shipping.

Assuming that isn't the case, I agree with StabbityBlkMage. Though you don't need to purchase a whole tub of Apoxie for a small fix. Hardware stores sell small tubes containing about 2oz of epoxy putty to use for household repairs. It's in the adhesives section. It works pretty much the same as Apoxie, only it has a faster cure time once mixed, usually something like 15 minutes.

For repair situations, instead of trying to smooth the putty while pliable, I prefer to apply it with just a fraction of a milimeter of excess. Then once it hardens, you can sand it perfectly flush.